Abstract
The Transcarpathia region of Ukraine is one of the most vulnerable regions for bioinvasions. There are five invasive and nine native species in the artificial water bodies of plain Transcarpathia. This study focused on the life-history traits of the Chinese sleeper Perccottus glenii Dybowski and pumpkinseed Lepomis gibbosus (L.). The standard length of the Chinese sleeper varied from 14.40 to 94.85 mm, and the total weight varied from 0.11 to 20.05 g. The standard length of pumpkinseed varied from 12.31 to 75.81 mm, and the total weight varied from 0.04 to 17.26 g. Both species form five age group populations dominated by young individuals and reach sexual maturity in their second year of life with a standard length of more than 40 mm. The combination of early maturation, rapid population turnover, and a broad size structure likely enhances the invasive success of both species under local conditions. These findings highlight the high adaptive potential of P. glenii and L. gibbosus and emphasize their capacity to establish stable populations, posing a long-term threat to native fish assemblages in artificial freshwater ecosystems of Transcarpathia.